Re: Protocol implementation split between base and derived class

FROM : Prachi Gauriar
DATE : Thu Dec 09 17:52:29 2004

On Dec 8, 2004, at 7:16 PM, Scott Hancher wrote:

> Can anyone comment on why XCode is throwing a compiler warning though? 
> This seems like an error to me.


The language in the Objective-C spec is somewhat ambiguous, but my 
interpretation of it is that the compiler is correct.

  @interface MyClass: MySuperClass <MyProtocol>
    ...
  @end

implies that MyClass *adopts* MyProtocol.  From the spec:  "A class is 
said to adopt a formal protocol if it agrees to implement the methods 
the protocol declares."  This leads me to believe that the class itself 
has to implement the methods in the protocol, i.e. adoption cannot be 
inherited.

Conforming to a protocol isn't as strong.  "A class is said to conform 
to a formal protocol if it (or a superclass) implements the methods 
declared in the protocol."

Finally, an incorporated protocol is what you used to solve your 
problem, a protocol within another protocol:

  @protocol MyProtocol <MyOtherProtocol>
    ...
  @end

A class can adopt an incorporated protocol by either "implementing the 
methods the protocol declares, or inheriting from a class that adopts 
the protocol and implements the methods."

See 
<http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/
LanguageOverview/chapter_3_section_7.html> for more details.

-Prachi